|
Hey all-
Thanks to the help of quite a few people on this board, I've done the following in the past few weeks to my '86 745T 218K miles:
New FPR
Checked ECT and knock sensor
Replaced timing belt & crank pulley, belt had slipped one tooth
Set base idle and set ignition timing to stock 12 degrees
Cleaned throttle body, tested and adjusted TPS, cut down WOT stop to enable butterfly to open fully.
The car definitely runs better. It feels, however, like it's not quite right.
When checking voltage at the O2 sensor, I get a very steady .7-.8 voltage reading. I've suspected that the O2 is bad, but when I rev the motor up a little and then release the throttle, the O2 voltage drops like a rock while the injectors shut down until idle resumes, and then we're back at .7-.8 volts.
Just for kicks I followed the excellent directions in the FAQ for building the CO test LED. Thanks to MVP, too. I checked it out and no surprise, the LED is always on, and the only time I've seen it go out (indicating lean condition) is during the drop from 2000 rpm to idle. No amount of fiddling with the AMM pot results in blinking or dead LED. I would think, however, the CO test point is really just feeding back what the ECU sees at the O2 sensor, so a bad O2 could look like no AMM adjustment.
I'm guessing one of three things-
1- unidentified rich mixture problem. The ECT tests fine hot and cold, along with anything I could find like it. The FPR is new. The fuel injector grounds are clean and tight.
2- Bad O2 sensor. I suppose it could be lazy, ready for replacement. The drop in voltage as engine speed drops is the only reason I haven't replaced it yet.
3- Bad AMM. I suppose if the AMM was bad, I could have a problem like slight enrichment, but I guess this is my last guess.
So if anyone thinks I've overlooked something big, or just has a few more tests I could run on the O2, I'd appreciate the input.
Thanks-
-Dylan
|
